Yes, these types of problems are mainly caused by addons. Firstly check that this problem is only with your Firefox browser or with another browser, like Internet Explorer. If it is with another ones too, then it is the fault of your system, try scanning it with your antivirus. Secondly, try running your Firefox in safe mode. At the top of the Firefox window, click the Firefox button, go over to the Help menu and select Restart with Add-ons Disabled.... Firefox will start up with the Firefox Safe Mode dialog. For more information, visit: Troubleshoot Firefox issues caused by malware Troubleshoot Firefox issues using Safe Mode

cje24576 wrote:

Could this be caused by one of my add-ons/ extensions?

Open the Help menu, either from the Firefox button or the menu bar, then choose Restart with Add-ons Disabled.

• Diagnose Firefox issues using Troubleshoot Mode

Also see

• How do I know that my Firefox problem is a result of malware?

Ok. I checked my other browser, and it's happening on that one as well. So, it's definitely a system problem. So, WHAT do I scan with my antivirus? Should I scan the whole computer? I did just change antivirus software from Norton 360 to Microsoft Security Essentials. Could changing my antivirus be causing this problem?

Do a malware check with several malware scanning programs on the Windows computer.
Please scan with all programs because each program detects different malware.
All these programs have free versions.

Make sure that you update each program to get the latest version of their databases before doing a scan.

• Malwarebytes' Anti-Malware:
  http://www.malwarebytes.org/mbam.php
• AdwCleaner:
  http://www.bleepingcomputer.com/download/adwcleaner/
  http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml
• SuperAntispyware:
  http://www.superantispyware.com/
• Microsoft Safety Scanner:
  http://www.microsoft.com/security/scanner/en-us/default.aspx
• Windows Defender:
  http://windows.microsoft.com/en-us/windows/using-defender
• Spybot Search & Destroy:
  http://www.safer-networking.org/en/index.html
• Kasperky Free Security Scan:
  http://www.kaspersky.com/security-scan

You can also do a check for a rootkit infection with TDSSKiller.

• Anti-rootkit utility TDSSKiller:
  http://support.kaspersky.com/5350?el=88446

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

I was wondering: should I perform all these scans while I'm using Mozilla/ the internet or does it matter? Also, regarding the "WinZip" software: it found something, but in order to "clean" the things it found, I have to purchase the full version of the software. Is there a free version of it?

Could you PLEASE respond to my questions?

Please understand that the people who answer questions here, for the most part, are other Firefox users volunteering their time (like me), not Mozilla employees or Firefox developers. That said, we will not be around 24/7.

The reason you haven't received a reply is because no one has responded since the 5th, therefore your question gets pushed down to make room for newer questions.

should I perform all these scans while I'm using Mozilla/ the internet or does it matter?

It shouldn't matter what you are doing when you run the scans. Just make sure a ton of windows aren't open.

Also, regarding the "WinZip" software: it found something, but in order to "clean" the things it found, I have to purchase the full version of the software. Is there a free version of it?

WinZip isn't a scanner. It's an extracting utility such as WinRAR or Windows Explorer. Where do you see WinZip at and what are you using it for?
On a related note, WinZip is only a trial software and expires after a certain number of days.

Removed JZip link. Unaware of malware/adware

Moses wrote:

You can use JZip

JZip is malware/adware. Use 7-Zip instead.

• http://www.7-zip.org

Gingerbread,

Thanks for the heads-up. I used JZip on my Windows box for a while and never suspected it of malware/adware. I've removed the link.